ruby-on-rails - Rails 查询播放列表推荐器

Question

基本上我有三个模型歌曲、播放列表和作业。

歌曲通过分配有许多播放列表，反之亦然。

我想编写一个查询来查找包含指定歌曲的每个播放列表。假设这首歌是由@song 指定的。

到目前为止，我有：

#find all the assignments that contain a song_id 

@commonAssignments = Assignment.where("song_id = ?", @data)
@commonPlaylists = #code to find playlists which contain any of the assignments found here

我想知道从这里去哪里，提前感谢您的帮助

Answer 1

#create an array of strings made up of playlist id's

@commonAssignments = Assignment.select(:playlist_id).where("song_id = ?", @data).map &:setlist_id

#then find all records associated
    @commonPlaylists = Playlist.find(@commonAssignments)